High voltage cardioverters and defibrillators today typically use an H-Bridge circuit configuration that discharges a charged capacitor for a Phase 1 descending biphasic truncated exponential (BTE) waveform through a diagonal pair of power transistors, MOSFETs, IGBTs, or any other switching devices, through the heart. A Phase 2 waveform is then switched on through a second diagonal transistor pair that delivers voltage and current through the heart, but in a reverse polarity as compared to the Phase 1 waveform. Both of the Phase 1 and Phase 2 waveforms are basically natural capacitive discharge waveforms based upon the “Tilt” equation:VC=VOe−t/RC  (I)
where VC is the voltage across a capacitor after a certain time period has elapsed; VO is the initial voltage across the capacitor before the discharging begins when it is connected in series with a resistor in a closed circuit; t is the period of time in seconds which has elapsed since the discharge process began; R is the resistance of the resistor to which the capacitor is connected in the circuit; and C is the capacitance of the capacitor. This voltage decay equation is the solution to a differential equation (based on energy balance) for constant resistance and capacitance (R and C), and the peak voltage and tilt decay are a function of the load impedance as the voltage is delivered through a load or heart muscle in the case of a high voltage cardioversion/defibrillation device or system. Pulse widths in existing ICDs are controlled by microcontroller commands which also contribute to the tilt angle of the waveform.
Class D amplifiers are very efficient and desirable to use. However, when Class D amplifier topologies or circuits are used, it is difficult to miniaturize the pulse width modulation (PWM) switching circuits as well as large and very large high current inductors and capacitors that are characteristic of Class D amplifiers. Therefore, a new approach is required to miniaturize these Class D topologies or circuits for use in implantable cardioverter defibrillator devices (ICDs), subcutaneous cardioverter defibrillator devices (SICDs), or other external or implantable devices without using the large or very large inductors and capacitors as low pass filters.